Capacitively coupled dielectric barrier discharge detector

Abstract

A gas detector designed for use with a gas chromatography system, or alone, comprising a tubular inner electrode, a tubular outer electrode coaxial with the inner electrode, and a dielectric tube axially between the inner electrode and the outer electrode. The dielectric tube serves as a dielectric barrier between the inner electrode and the outer electrode. There is a longitudinal gap between the left end of the outer electrode and the right end of the inner electrode, and a sufficient voltage is applied across the gap between the electrodes to create an electrical discharge which emits light from a gas passing through the gap. The light is then detected and analyzed to determine the chemical constituents of the gas passing through the gap.

1 . A gas detector comprising:
 (a) a tubular inner electrode with a left end and a right end, an inside and an outside;   (b) a dielectric tube coaxial with the inner electrode, the dielectric tube with a left end and a right end, an inside and an outside, the right end of the inner electrode inside the left end of the dielectric tube;   (c) a tubular outer electrode coaxial with the inner electrode and the dielectric tube, the outer electrode with a left end and a right end, an inside and an outside, the right end of the dielectric tube inside the left end of the outer electrode;   (d) the inner electrode adapted to allow a gas to flow therethrough, and the dielectric tube adapted to allow the gas to flow therethrough;   (c) the dielectric tube serving as a dielectric barrier between the inner electrode and the outer electrode;   (d) a longitudinal gap between the left end of the outer electrode and the right end of the inner electrode;   (e) the electrodes adapted to connect to an AC voltage supply creating a voltage between the outer electrode and the inner electrode, the voltage acting across the longitudinal gap and through the dielectric barrier, the voltage creating a continuous plasma discharge within the gas; and   (f) a sensor adapted to detect changes in optical properties of the gas as it passes through the gap.   
   
   
       2 . The gas detector of  claim 1  wherein the outer electrode comprises a metallic or other conductive coating on the outside of the dielectric tubing. 
   
   
       3 . The gas detector of  claim 1  wherein the outer electrode comprises a metallic or other conductive coating on the inside of the dielectric tubing. 
   
   
       4 . The gas detector of  claim 1  wherein the sensor detects changes in optical properties by detecting a change in light emission. 
   
   
       5 . The gas detector of  claim 4  wherein the sensor is a photodiode. 
   
   
       6 . The gas detector of  claim 4  wherein the sensor is a spectrometer. 
   
   
       7 . The gas detector of  claim 4  wherein a fiberoptic cable carries light from a first end of the fiberoptic cable at an area communicating with the gap to a second end of the fiberoptic cable communicating with the sensor. 
   
   
       8 . The gas detector of  claim 7  wherein the fiberoptic cable passes through an opening in the inner electrode. 
   
   
       9 . The gas detector of  claim 7  wherein the fiberoptic cable passes through an opening in the dielectric tube. 
   
   
       10 . The gas detector of  claim 1  additionally comprising a means for generating a graph from the changes detected in optical properties of the gas. 
   
   
       11 . The gas detector of  claim 1  additionally comprising a heater adapted to maintain the entire detector at an elevated temperature. 
   
   
       12 . The gas detector of  claim 1  wherein the AC voltage supply provides about 1 to 100 kilovolts across the dielectric barrier between the outer electrode and the inner electrode. 
   
   
       13 . The gas detector of  claim 12  wherein the inner electrode has an inner diameter of about 10 to 1000 microns. 
   
   
       14 . The gas detector of  claim 13  wherein the dielectric tube has an inner diameter that closely fits the outer diameter of the inner electrode, the dielectric tube being about 50 to 1000 microns thick. 
   
   
       15 . The gas detector of  claim 14  wherein the outer electrode is a conductive coating directly applied to the dielectric tube. 
   
   
       16 . The gas detector of  claim 14  wherein the outer electrode is made from capillary tubing that closely fits the dielectric tube. 
   
   
       17 . The gas detector of  claim 16  wherein the dielectric tube is made of glass, ceramic, or quartz. 
   
   
       18 . The gas detector of  claim 17  wherein the outside of the outer electrode is covered with a dielectric. 
   
   
       19 . The gas detector of  claim 17  wherein a dilution gas is supplied through the dielectric tube. 
   
   
       20 . The gas detector of  claim 17 , wherein a dilution gas is supplied through the inner electrode. 
   
   
       21 . The gas detector of  claim 1 , wherein the gas flows into the inner electrode at the left end of the inner electrode and out of the inner electrode at the right end of the inner electrode, the right end of the inner electrode communicating with the left end of the dielectric tube, the gas then flowing from the left end of the dielectric tube and out the right end of the dielectric tube. 
   
   
       22 . A gas chromatography system comprising:
 (a) an injection chamber for introducing a sample;   (b) a column separator through which the sample flows as a gas;   (c) a tubular inner electrode with a left end and a right end;   (d) a dielectric tube with a left end and a right end, the right end of the inner electrode coaxially within the left end of the dielectric tube;   (e) a tubular outer electrode with a left end and a right end, the right end of the dielectric tube coaxially within the left end of the outer electrode;   (f) the inner electrode adapted to allow a gas to flow therethrough, and the dielectric tube adapted to allow the gas to flow therethrough;   (g) the dielectric tube serving as a dielectric barrier between the inner electrode and the outer electrode;   (h) a longitudinal gap between the left end of the outer electrode and the right end of the inner electrode;   (i) the electrodes adapted to connect to an AC voltage supply creating a voltage between the outer electrode and the inner electrode, the voltage acting across the longitudinal gap and through the dielectric barrier, the voltage creating a continuous plasma discharge within the gas; and   (j) a sensor adapted to detect changes in optical properties of the gas as it passes through the gap.   
   
   
       23 . The gas chromatography system of  claim 22  wherein the outer electrode comprises a metallic coating on the outside of the dielectric tubing. 
   
   
       24 . The gas chromatography system of  claim 22  wherein the outer electrode comprises a metallic or other conductive coating on the inside of the dielectric tubing. 
   
   
       25 . The gas chromatography system of  claim 22  wherein the sensor detects changes in optical properties by detecting a change in light emission. 
   
   
       26 . The gas chromatography system of  claim 25  wherein a fiberoptic cable carries light from a first end of the fiberoptic cable at an area communicating with the gap to a second end of the fiberoptic cable communicating with the sensor. 
   
   
       27 . The gas detector of  claim 26  wherein the fiberoptic cable passes through an opening in the inner electrode. 
   
   
       28 . The gas detector of  claim 26  wherein the fiberoptic cable passes through an opening in the dielectric tube. 
   
   
       29 . The gas chromatography system of  claim 22  additionally comprising a means for generating a graph from the changes detected in optical properties of the gas. 
   
   
       30 . The gas chromatography system of  claim 22  additionally comprising a heater adapted to sustain the gas at a constant temperature. 
   
   
       31 . The gas chromatography system of  claim 22  wherein the AC voltage supply provides about 1 to 100 kilovolts across the dielectric barrier between the outer electrode and the inner electrode. 
   
   
       32 . The gas chromatography system of  claim 31  wherein the inner electrode has an inner diameter of about 10 to 1000 microns. 
   
   
       33 . The gas chromatography system of  claim 32  wherein the dielectric tube has an inner diameter that closely fits the outer diameter of the inner electrode, the dielectric tube being about 50 to 1000 microns thick. 
   
   
       34 . The gas chromatography system of  claim 33  wherein the outer electrode is a conductive coating directly applied to the dielectric tube. 
   
   
       35 . The gas chromatography system of  claim 33  wherein the outer electrode is made from capillary tubing that closely fits the dielectric tube. 
   
   
       36 . The gas chromatography system of  claim 35  wherein the dielectric tube is made of glass, ceramic, or quartz. 
   
   
       37 . The gas chromatography system of  claim 36  wherein the outside of the outer electrode is covered with a dielectric. 
   
   
       38 . The gas chromatography system of  claim 37  wherein a dilution gas is supplied through the dielectric tube. 
   
   
       39 . The gas chromatography system of  claim 37 , wherein a dilution gas is supplied through the inner electrode. 
   
   
       40 . The gas chromatography system of  claim 18 , wherein the gas flows into the inner electrode at the left end of the inner electrode and out of the inner electrode at the right end of the inner electrode, the right end of the inner electrode communicating with the left end of the dielectric tube, the gas then flowing from the left end of the dielectric tube and out the right end of the dielectric tube.